They're both correct. At gatherings you would simply say "thanks for coming" but if the person is coming from somewhere north you can also say "thanks for coming down."

Regardless of the direction your guests come from you can say "thanks for coming out," but it's more natural if you have guests from all over or if they don't live nearby (or if they had to travel during a storm!) I mostly hear "thanks for coming out" at public events (concerts, sports) since people there come from all over.